Spiral wound membrane element for high temperature filtration

ABSTRACT

A spiral wound membrane module is suitable for use with high temperature water that may also have a high pH, for example steam injection produced water. The module uses a membrane with a polyphenylene sulfide (PPS) backing material. The feed spacer of the module may be made from polyphenylene sulfide (PPS) or ethylene chlorotrifluoroethylene (ECTFE). The permeate carrier may be made of a woven nylon (i.e. nylon 6, 6) fabric coated with high temperature epoxy. The core tube and anti-telescoping device may be made of polysulfone. In some examples, the module may be used at a temperature of up to 130° C. Optionally, the module may be used at a pH of 9.5 or more. In a filtration method, the module may be operated at a pressure in the range of 150 to 450 psi. The module may be operated at a generally constant pressure.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/961,906, filed Jul. 13, 2020, which is a National Stage Entry ofInternational Application No. PCT/US2019/017271, filed Feb. 8, 2019,which claims the benefit of U.S. Application Ser. No. 62/629,286, filedFeb. 12, 2018.

FIELD

This specification relates to spiral wound membrane elements or modulesuseful, for example, for reverse osmosis or nanofiltration, to methodsand apparatus for treating high temperature fluids, and to methods andapparatus for treating produced water for re-use in a steam boiler orgenerator, for example in a steam assisted gravity drainage (SAGD) orother high temperature produced water treatment process.

BACKGROUND

The following discussion is not an admission that anything discussedbelow is citable as prior art or common general knowledge.

In various forms of oil and gas production, produced or other waterstreams are created that must be treated for disposal or re-use. Forexample, in a bitumen mining process known as Steam Assisted GravityDrainage (SAGD), steam is produced in a boiler or generator and injectedinto bitumen bearing soil. The steam reduces the viscosity of thebitumen allowing a mixture of water and bitumen to flow to a productionwell. After this mixture is extracted, most of the oil is removed in aninitial primary oil-water separation step. Other enhanced oil recoverymethods used to extract heavy crude oil with steam injection, such asCyclic Steam Stimulation (CSS) and Steam Flooding, produce similar hotmixtures of oil and water.

The water remaining after primary oil-water separation, called producedwater, is hot and often alkaline with a high pH. The produced water istreated through various unit operations to make it suitable for re-usein generating steam. The produced water may contain, for example,residual oil and suspended, emulsified and dissolved solids (organic andinorganic), such as silica. The concentration of dissolved solids may beup to about 6,000 mg/L total dissolved solids (TDS) and the silica maybe at or near the limit of solubility. Oil may be removed from theproduced water by a second oil-water separation step such as gasflotation or a ceramic or walnut shell filter. Hot or warm limesoftening may be used to remove silica and hardness. Particlefiltration, for example through an anthracite bed, may be used to reducetotal suspended solids. Strong or weak acid cation exchange softenersmay be used to further reduce hardness.

After treatment, the produced water can be re-used to generate steam.The steam generators used in SAGD operations commonly include a OnceThrough Steam Generator that produces about 80% steam (vapour) and about20% liquid droplets. The liquid fraction is removed from the steam in ablowdown stream before the steam is injected into the bitumen deposit.The OTSG blowdown water is further processed or, where permitted,disposed for example in a tailings pond or by deep well injection. Inanother option, the produced water is treated in an evaporator and thecondensate is converted to steam in a packaged boiler. One treatmentoption for evaporator or boiler blowdown is to evaporate or vaporizegenerally pure water from the blowdown, for example in a brineconcentrator or thermal crystallizer or both, to produce dried solidsfor disposal.

Ceramic membranes have been proposed to supplement or replace one ormore treatment units in a produced water treatment system. However,ceramic membranes are generally expensive and can be difficult to clean.U.S. Pat. No. 8,940,169 describes a spiral wound membrane modulesuitable for use with high temperature water that is also very alkalineor has a high pH, for example SAGD produced water. The module uses apolyamide-based membrane with a polysulfone or polyethersulfone backingmaterial. For other components, the module uses primarily one or moreof, EPDM; polyamide; polyphenylene oxide; polyphenylene sulfide;polysulfone; polyethersulfone; polysulfonamide; polyvinylidene fluoride(PVDF); mylar; fiberglass; and, epoxy. In one example, a module uses aPVDF feed spacer, a nylon permeate spacer and a polysulfone center tube.

INTRODUCTION

The following introduction is intended to introduce the reader to thedetailed description to follow and not to limit or define any claimedinvention.

A primary purpose of the produced water treatment steps described aboveis to provide water of suitable quality to the steam generator. Silicaand hardness in the raw produced water in particular would rapidly foula steam generator. However, even after a two-stage process of limesoftening followed by cation exchange softening, the water reaching anOTSG in an existing SAGD operation may still have near 1 mg/L ofhardness. Treated produced water in an existing SAGD operation may alsocontain 100 to 2,000 mg/L of dissolved organics when it reaches theOTSG. As a result of the remaining contaminants in re-used producedwater, a foulant layer builds up on OTSG walls over time. Further,organic and other contaminants are concentrated in blowdown water, whichin some cases may impede using a crystallizer to treat the blowdown.

By using a spiral wound membrane element or module upstream of the OTSGor other boiler, either in place of or in combination with a cationexchange softener, the silica concentration, hardness and TDS ofproduced water can be reduced. The spiral wound membrane element mayhave a membrane in the ultrafiltration (UF), nanofiltration (NF) orreverse osmosis (RO) range and elements with membranes in two or more ofthese ranges may be placed in series. To remove hardness, a set of oneor more spiral wound membrane elements preferably ends with an elementwith a NF or RO membrane. The very low concentration of contaminants,particularly hardness, in NF or RO permeate would reduce OTSG fouling.Using an RO membrane in particular would also allow a conventional highpressure steam boiler (i.e. a packeged boiler), with a lower blowdownratio, to be used in place of an OTSG, without the RO permeate requiringprior treatment in an evaporator. A spiral wound membrane module mayalso be used to concentrate steam blowdown water, either to reduce thevolume of water to be disposed of, to replace a brine concentrator, orto otherwise pre-condition blowdown water for treatment in acrystallizer.

The produced water, however, has a very high temperature and asignificant concentration of silica. Because the produced water isintended for re-use to produce steam, the process is more energyefficient if the produced water is not cooled to facilitate anytreatment process. The produced water may therefore move through allprocess steps at a temperature of 90 degrees C. or more. In addition tothe high temperature, it is helpful if the modules are also stable athigh pH, for example 9.5 or more, 10.5 or more, or 11.5 or more.Stability at high pH can facilitate cleaning, for example using caustic,which is preferably done at the operating temperature of 90 degrees C.or more. Operation at high pH may also inhibit silica fouling, forexample by increasing the pH of the membrane feed water in a mannersimilar to the HERO™ process as practiced by Suez Water Technologies &Solutions for operation in high-silica waters.

A spiral wound module is described herein that is suitable for use withhigh temperature water, which may be produced water or another type ofhigh temperature water. Optionally, the module may also be suitable foruse with water that is alkaline or has a high pH for prolonged periodsof time. For example, the module may operate at a temperature of 90degrees C. (190 degree F.) or more and a pH of 9.5 or more, 10.5 or moreor 11.5 or more. Optionally, the module is adapted to be cleaned with ahot caustic solution.

The module may be used, for example, for treating SAGD or other steaminjection produced water. The module uses a combination of materials forits various components that is adapted to operate under theseconditions.

The module may use membranes with a polyphenylene sulfide (PPS) backing.For example, the backing may be a non-woven fabric made of PPS fibers.To complete the membrane, an intermediate polysulfone orpolyethersulfone layer may be cast on the backing. The intermediatelayer may have pores in the ultrafiltration range. A further RO or NFlayer is cast on the intermediate layer. For example, an RO layer may bemade from a polyamide, for example by interfacial polymerization.

The feed spacer of the module may be made from polyphenylene sulfide(PPS) or ethylene chlorotrifluoroethylene (ECTFE). The permeate carriermay be made of a woven nylon (i.e. nylon 6, 6) fabric coated with hightemperature epoxy. The core tube and anti-telescoping device may be madeof polysulfone.

The outer cover (also called the outer wrap) may be made of fiberglassin an epoxy resin. Epoxy is also preferred over polyurethane as anadhesive inside the module. Various smaller internal components may bemade of one or more of the plastics listed above, a durable rubber suchas ethylene propylene diene Monomer (M-class) rubber (EPDM), or otherdurable materials such as mylar film.

The module may be used to filter water at high temperature andoptionally high pH. For example, the module may be used at a temperatureof 90° C. or more, or 100° C. or more, optionally up to 130° C.Optionally, the module may be used at a pH of 9.5 or more. In afiltration method, the module may be operated at a pressure of about 300psi, for example 150 psi to 450 psi. The module may be operated at agenerally constant pressure. The module may be used to filter producedwater. Permeate from the module may be sent to a boiler, for example toproduce steam for injection into a heavy oil deposit.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a partially cut away isometric view of a spiral woundmodule.

DETAILED DESCRIPTION

A spiral wound membrane module (alternatively called an element) can bethought of as being composed of two or more groups of materials. Thefirst group is the membrane. The membrane is the functional componentwithin the module that does the work of separating the feed water intofiltered (permeate) and waste (brine or retentate) streams. A membraneis typically comprised of three layers of decreasing porosity startingwith a fabric (i.e. nonwoven) backing, then a supporting or intermediatelayer, and then a separation or membrane layer. The supporting layer maybe made of polysulfone, made porous by casting a dope and forming poresby a phase-inversion process. The separation layer may be a polyamidelayer made by interfacial polymerization.

A typical membrane might not fail when operated at 90° C. for a shortperiod of time, but the lifetime of the materials can be significantlyshortened by high temperature operation, especially when operating athigh pH. For example, in tests by the inventors poly(butylterephthalate) was almost dissolved and poly(ester terephthalate) wasmaterially degraded after soaking in water at 130° C. and a pH of 9.5for two weeks. Polyesters such as these are commonly used as membranebacking layers. In contrast, the polysulfone and polyamide layers insamples of typical membranes survived exposure to water at 130° C. and apH of 9.5 for two weeks, as did samples of polyphenylene sulfide (PPS).

In some embodiments, a module is constructed of materials to allowoperation at 90° C. or more or 100° C. of more. Optionally, the modulemay be constructed to allow operation at a temperature up to 130° C.Optionally the module may operate at up to a pH of 9.5 or more.

Examples of high temperature membranes were made having a non-wovenbacking substrate of polyphenylene sulfide. Polysulfone UF films werecast on the backing from a dope solution of 22% (wt.) polysulfone inn,n-dimethylformamide, with 1% (wt.) lithium bromide. The UF films werecast with a 0.010″ gap doctor blade onto a sheet of the backingsubstrate that was taped to a glass plate. The cast films were submergedinto a room temperature de-ionized (DI) water bath to quench. They werestored in the water bath overnight, after which the water was changedand they were stored in the water batch for about another 5 days.Casting took place under ambient conditions (room temperature, about 10%humidity) under a laboratory fume hood. After being removed from thewater bath, excess water was removed from the surface of the UF filmsand they were coated with a polyamide RO layer.

Coupons of the membranes with PPS backing were soaked in a syntheticfeed solution at 135° C. for 2 weeks in an autoclave. The feed solutioncontained 200 ppm sodium chloride, 20 ppm calcium chloride and 200 ppmsilica and had a pH of 9.5. Samples were removed from the autoclave atthe end of the first and second weeks and tested for flux (A-value) andNaCl selectivity with a crossflow test procedure.

The coupons had an average A-value of 3.79 and 46% salt passage. AnA-value of 3.79 is roughly equivalent to a full-sized (8-inch diameter)element with a permeate flow of 975 LPH. This flux is reduced by about40% from typical commercially available modules. The high salt passageis believed to be the result of pinhole defects in the coupons. It isexpected that optimizing the membrane making process would likely yieldimproved flux and selectivity, but the coupon results demonstrate thatuseful membranes were produced on the PPS backing.

A second group of materials includes the feed spacers, permeatecarriers, core tube and anti-telescoping device which serve to give themodule structure and support while creating the flow paths for waterthrough the module. These components are typically fabricated fromcommodity plastics such as polyester, polypropylene and ABS. Thesematerials are not designed for use at elevated temperatures and maybegin to fail at even moderately elevated temperatures, for example 60or 70° C.

Examples of materials suitable for operation at high temperature,optionally above 100° C. are shown in Table 1.

TABLE 1 Component Material Membrane Polyamide UF Support Polysulfone orPolyethersulfone Backing PPS Permeate Carrier Epoxy-coated nylon knittedfabric Feed Spacer ECTFE or PPS Core Tube Polysulfone Adhesive Epoxy ATDPolysulfone

Examples of module structural elements and adhesive samples wereimmersed in water at at 135° C. and a pH of 9.5 for a minimum of 2weeks. Adhesive samples were configured in a lap sheer format betweenlayers of polyester backing and tested for tensile strength. All othermaterials were inspected visually for changes in shape and for massloss.

Module structural elements tested included, feed spacers made from PPSand ECTFE (HALAR™); coated PET permeate carrier; high temperatureepoxies; and core tubes made of polysulfone; polyproylene and EPTFE feedspacer; and, Polyset polyurethane adhesive. All of the componentssurvived the test.

FIG. 1 shows a spiral wound membrane module 10. One primary component isthe separation membrane 12, which is formed into a flat sheet. Otherprimary internal components are a feed channel spacer 14, a permeatespacer (or permeate collection material) 16, a permeate collection tubeor center tube 18 and an end surface holder or anti-telescoping device20 at each end of the module 10. The membrane 12 is arranged to form anenvelope around the permeate spacer 16. The edges of the envelope aresealed except that at an inside edge the permeate spacer 16 is open toperforations 22 of the center tube 18. The feed channel spacer 14 isplaced over the envelope. The envelope and feed channel spacer 14 arewound around the center tube 18. Feed water can access the surface ofthe membrane 12 by flowing into the edge of and across the feed channelspacer 14. Permeate passes through the membrane 12, then flows throughthe permeate spacer 16 and center tube 18 to leave the module 10.Concentrate flows out of the downstream edge of the feed channel spacer14 to leave the module. The anti-telescoping devices 20 are glued ortaped to the center tube 18 and also held in place by an outer wrap 24.The anti-telescoping devices 20 prevent the envelopes from being pushedalong the length of the center tube 18 by the feed water. An outer wrap24 surrounds the envelopes to keep them from unwinding in use.

One or more of various other components may also be present in themodule 10. For example, the membrane 12 typically comprises a membranesupport or backing layer. The envelopes may be sealed with an adhesive.In a multi-stage module, two or more center tubes 18 may be connected inseries by element interconnectors. The module typically has O-rings,brine seals or other end-seal gaskets and other seals. Folds in theenvelope may be reinforced with a tape or film. A film or tape may alsobe used to provide an inner wrap. Tape may also be used to help hold theanti-telescoping devices 20 in place.

The membrane 12 may be a polyamide-based membrane with a backingmaterial of, for example, PPS. The backing material may be coated withan intermediate layer of polysulfone or polyethersulfone, made porous bya phase inversion process. Thereafter, the surface of the coated backingmaterial is coated with a reverse osmosis or nanofiltration membrane.

In other components, the membrane module 10 makes use of one or more ofthe following materials, or blends of the following materials: polyamide(PA, nylon); polyphenylene oxide (PPO, NORYL™); polyphenylene sulfide(PPS); polysulfone (PSO); polyethersulfone (PES); polysulfonamide; and,polyvinylidene fluoride (PVDF), EPDM, fiberglass, epoxy and mylar.Polypropylene may be used in minor components such as a backing for atape.

In an example of a spiral would module 10 intended for use in treatingSAGD or other high temperature produced water. The feed channel spacer14 is made of PPS or ethylene chlorotrifluoroethylene (ECTFE). Thepermeate spacer 16 is made from a knitted yarn of nylon 6-6 and epoxy.Epoxy is used for an adhesive in other parts of the module 10. Thecenter tube 18 is extruded from polysulfone. An element interconnectoris also extruded from polysulfone. The anti-telescoping device 20 isinjection molded from polysulfone. The outer wrap 24 is made offiber-reinforced plastic, for example fiberglass embedded in epoxy. Aninner wrap is made from a polypropylene backed pressure sensitiveadhesive (PSA) tape. The same tape is used on other parts of the module10 requiring tape. Creased mylar film is used for a fold reinforcement.A concentrate seal and O-rings are made from molded EPDM rubber.

Optionally, the center tube of the module 10 may be provided with 3 ormore rows of holes having a diameter of 0.1″ or less, or perforations ofother shapes having an equivalent area, for example 4 rows of 0.063″diameter holes. The module 10 may also be rolled under a tension of 20psig or more, for example about 25 psig. The central tube 18 is mountedin a driven chuck assembly that is first used to roll up all of theleaves or elements of the module. Inner wrap tape is then wrapped aroundthe element. The tension of the tape inner wrap is controlled by thetension at which the tape is allowed to unwind from a roll that it ismounted on. The tension and numerous small holes assist the heatedmaterials in resisting mechanical stresses.

While the module as described above is suitable for use in service withwater having a high temperature and pH, it may also be used with waterunder other conditions. The ability of the module to withstand extremeconditions can also be used when cleaning the module. In particular, themodule may be cleaned with a hot caustic solution, for example a highlyconcentrated and heated solution of NaOH. The solution may be used, forexample, according to known clean in place procedures. However, due toan increased reaction rate relative to typical cleaning solutions, oneor more of the time, energy, water, or other consumables required forcleaning may be reduced.

U.S. Pat. No. 8,940,169 is incorporated herein by reference.

We claim:
 1. A spiral wound membrane module comprising, a membraneenvelope comprising a membrane and a permeate spacer; a feed spaceradjacent the membrane envelope; a center tube, wherein the membraneenvelope and feed spacer are wrapped around the center tube; and, ananti-telescoping device attached to the center tube beside the membraneenvelope and feed spacer, wherein the membrane material comprises apolyphenylene sulfide backing or the feed spacer comprises ethylenechlorotrifluoroethylene or polyphenylene sulfide.
 2. The spiral woundmembrane module of claim 1 wherein the membrane comprises apolyphenylene sulfide backing.
 3. The membrane module of claim 2 whereinthe membrane further comprises an intermediate polyethersulfone layer.4. The membrane module of claim 3 wherein the membrane further comprisesa polyamide separation layer.
 5. The membrane module of claim 1 whereinfeed spacer comprises ethylene chlorotrifluoroethylene or polyphenylenesulfide.
 6. The membrane module of claim 2 wherein the feed spacercomprises ethylene chlorotrifluoroethylene or polyphenylene sulfide. 7.The membrane module of claim 6 wherein the permeate carrier comprises anylon fabric coated with epoxy.
 8. The membrane module of claim 6wherein the core tube is made of polysulfone.
 9. The membrane module ofclaim 8 wherein the anti-telescoping device is made of polysulfone. 10.A filtration process comprising steps of, providing a membrane moduleaccording to claim 1; feeding water to the membrane module at atemperature in the range of 90° C. to 130° C.
 11. The process of claim10 comprising feeding water to the membrane module at a temperatureabove 100° C.
 12. The process of claim 10 comprising feeding water tothe membrane module at a pH of 9.5 or more.
 13. The process of claim 10comprising feeding produced water to the membrane module.
 14. Theprocess of claim 10 comprising feeding water to the module at a pressurein the range of 150 psi to 450 psi.
 15. The process of claim 14comprising feeding water to the module at a generally constant pressure.